The invention relates to a seat suspension apparatus including one or more spring which produces a cushioning effect against a user, and more particularly, to such apparatus in which the resilience of the spring and the elevation of the seat are adjustable.
A seat suspension apparatus of the kind described is mounted under a driver's seat of a heavy weight road vehicle such as goods vehicles, for example. Examples of conventional seat suspension apparatus are schematically illustrated in FIGS. 1a, 1b and 1c. The arrangement shown in FIG. 1a includes a pair of frames 30, 31, pivots 32, 34 fixedly mounted on the frame 30, pivots 33, 35 fixedly mounted on the frame 31, and a pair of connecting links 36, 37 which are pivotally mounted on the pair of pivots 32, 33 and 34, 35, respectively. An arm 38 is secured to the pivot 35 and has its free end connected with one end of a spring 39, the other end of which is connected with a threaded end of a handle 41 through a rotatable fastener 40. With this seat suspension apparatus, when a load (seating weight) is applied to a seat plate 42 secured to the frame 31 in a direction indicated by a thick arrow, the links 36, 37 turn clockwise until the tension of the spring 39 is balanced with the seating load. By turning the handle 41 to change the tension of the spring 39, the links 36, 37 can be turned either counter-clockwise or clockwise to change the elevation of the seat plate 42 and to vary the degree of a cushioning effect.
In the arrangement shown in FIG. 1b, the pivot 34 is rotatably mounted on the frame 30 and is fixedly connected with the link 37, with the arm 38 being secured to the pivot 34. Again, the handle 41 is turned to change the tension of the spring 39 in order to change the elevation of the seat plate 42.
In the arrangement shown in FIG. 1c, lower frame 30 is secured to a floor and carries pivots 32, 34 which are coupled with both links 36, 37. A similar seat suspension apparatus is disclosed in British Patent Specification No. 1,208,051 (Intl. Class B 60 nl/06, Complete Specification published Oct. 7, 1974).
A common problem to these conventional seat suspension apparatus is an increased height a from the floor and an increased back-and-forth stroke b (see FIG. 1c) through which the seat must be moved. Specifically, in the arrangements shown in FIGS. 1a and 1b, the height a is necessarily greater than the spacing between the pivots 32, 34. With the arrangement of FIG. 1c, the lowermost position or the height a of the suspension must be maintained at a relatively high level since the parallelism of the seat plate 42 cannot be maintained if the latter is allowed to be lowered until all of the pivots 32, 34, 33, 35 are aligned on a line in response to the weight of a seat occupant and/or vibrations or shocks applied by the vehicle. The back-and-forth stroke b is also high because the pivot 35 follows a circular locus which is struck from the pivot 34 and the link 37 angularly moves above its horizontal position. In this manner, the increased magnitude of the height a and the back-and-forth stroke b of the suspension apparatus required an increased space margin around the driver's seat of the vehicle.
Another problem which is experienced with conventional seat suspension apparatus is the fact that a seat occupant must assume a slouched position to turn the handle which is located on the front side of the seat in order to adjust the tension of the spring. Furthermore, the handle must be turned several times in order to reach a proper elevation. It is cumbersome for the seat occupant to assume such position or to operate the handle in this manner, in particular for a driver who is forced to leave his proper seating position. Another type of seat suspension is disclosed in U.S. Pat. No. 2,357,825.